Motion detection by visual processing is well known in the art. For example, U.S. Pat. No. 6,504,479 discloses various systems and methods for motion detection. Similarly, thermal imaging via infrared (IR) is well known in the art. For example, an intruder alert system that employs IR is described in U.S. Pat. No. 5,825,413. Each, however, suffers from drawbacks that produce sub-optimal motion detection and/or intruder alert systems.
Conventional systems, particularly those employed in a visually noisy environment, may generate false positives (e.g., false alarms). For example, a motion detector outside a barn door may trigger an alarm due to the activity of a raccoon, or, on a windy night, when a tarpaulin covering a nearby woodpile flaps in the wind. Similarly, a heat detector inside a warehouse may trigger an alarm due to the activity of a rat, or a motion detector may alarm when the air conditioning system engages and blows scrap paper across the detection system field of view. False alarms may also be generated due to changing light conditions that produce apparent motion and/or thermal signature changes. By way of illustration, the rising sun may generate a thermal signature change directly and/or in items reflecting the sun. Furthermore, shadows and refractions may cause thermal signature changes.